Transport devices are hitherto known as described, for example, in Japanese Patent No. 4054191.
The transport device described in Japanese Patent No. 4054191 includes a drive wheel driven by a motor to rotate at constant speed, a plurality of suction members each attached to the drive wheel via a crank arm and configured to hold processed articles, and a base part that rotatably supports the drive wheel.
Each of the crank arms is attached to the drive wheel such as to be rotatable around a rotation center axis that is parallel to that of the drive wheel. A cam roller is provided for changing speeds, at a position away from the rotation center of each crank arm, to be movable along a speed-changing cam groove formed in the base part. The speed-changing cam groove is formed eccentrically to the center of the drive wheel.
Thus, the distance from the center of the drive wheel to each speed-changing cam roller changes periodically in accordance with the positional relationship between the speed-changing cam roller and the speed-changing cam groove. Namely, the crank arm moves forward or backward in the rotating direction of the drive wheel as the drive wheel rotates. Angular velocity of each of suction member changes due to this movement (swing) as the drive wheel rotates.
This way, with the transport device described in Japanese Patent No. 4054191, processed articles received at a receiving position are transported to a transfer position, with the speed of the processed articles being varied between the receiving position and the transfer position.
However, in this transport device described in Japanese Patent No. 4054191, the speed change of each suction member is achieved by a mechanical configuration (speed-changing cam roller and cam groove). Therefore, it is difficult to set a plurality of speeds of the processed articles at the transfer position.
More specifically, It is conceived that the processed articles could be transported at a plurality of speeds by varying the angular velocity of the motor that rotates the drive wheel described in Japanese Patent No. 4054191. However, changing the angular velocity of the drive wheel that carries a plurality of suction members requires a large torque, and a motor that can be accelerated and decelerated in a short time would be needed. Motors that can satisfy these conditions are hard to be secured.
It would be possible to set a plurality of speeds of the processed articles at the transfer position by driving the motor at a constant speed higher, or lower, than usual in the transport device described in Japanese Patent No. 4054191. This, however, would lead to a variation in the quantity of transported articles per unit time, because changing the motor speed would vary the cycle of each suction member (processed article) arriving at the transfer position.
Therefore, in order to change speed of each suction member while maintaining the transport quantity per unit time in the transport device of Japanese Patent No. 4054191, it would be necessary to prepare many kinds of the mechanical configurations described above for each of several target speeds. This would increase the facility cost, and also the operation time, since it is necessary to change the mechanical configurations every time the speed is changed.